Preparation Of Ultrathin And Stable Lamellar Composite Membrane And Its Application In Hexane Dewaxing

In recent years,with the rapid development of social economy,the global demand and consumption of polyethylene products are increasing significantly.How to deal with a large number of by-products of polyethylene production in an energy-saving and efficient way is a major problem in the environment-friendly situation.The effective solution of this problem also has a far-reaching impact and great significance on the development and prosperity of the petroleum and petrochemical industry.As a new separation technology,membrane separation technology has many outstanding advantages,such as high efficiency,energy saving,environmental protection,simple operation and so on.It has become one of the effective ways to solve the problem of social and economic sustainable development.The two-dimensional lamellar membrane has become a hot research direction of new nanofiltration membrane because of its ordered lamellar structure,easy to control chemical microenvironment,efficient molecular transfer characteristics and easy ultrathin preparation.In this study,the precise preparation of high-performance two-dimensional lamellar composite membrane and its application in the dewaxing of slurry polyethylene as the main research content,developed an ultrathin and stable GO-PEI lamellar composite membrane,and tried to apply it in the industrial application of slurry polyethylene dewaxing.The GO-PEI organic-inorganic lamellar composite membrane developed by electrostatic atomization technology can have high nanofiltration performance while maintaining high stability of structure and long-term operation,which can solve the trade-off effect between the permeance and rejection existing in traditional nanofiltration membrane to a certain extent.In addition,we develop the GO-PEI try used in slurry polyethylene dewaxing industrial application,while maintaining high paraffin molecular rejection rate at the same time,raised the permeance of paraffin solution by 25 times,for high efficiency low energy consumption of membrane separation technology used in slurry polyethylene production process in the solvent dewaxing recycling provides the application prospect.Specific research contents and main conclusions are as follows:（1）A lamellar organic-inorganic composite membrane consisting of graphene oxide（GO）and polyethylenimine（PEI）was prepared by two-needle electrostatic atomization.GO nanosheets serve as the skeleton to ensure ultrathin and defect-free membrane structure,while PEI cross-linked adjacent GO nanosheets keeps stable membrane structure.Importantly,this membrane achieves rapid polar solvent penetration:the permeance of water and acetone reach 46.2 L m^-2 h^-1 bar^-1 and 146.8 L m^-2 h^-1 bar^-1,respectively,which are superior to most reported GO-based membranes.At the same time,ordered cross-linked interlayer channels provide precise particle size rejection for industrial dyes（larger than 1.6 nm）with a rejection rate of over 96%.It is worth noting that the lamellar composite membrane has excellent structure,operation,pressure and cycle stability,which is difficult to achieve the traditional laminated membrane.（2）Commercial polyamide organic solvent nanofiltration membrane was used to test the nanofiltration performance of hexane and paraffin solution.The results showed that the fluxes of commercial membranes NF-7（with interception molecular weights MW=1500～2000）and NF-8（MW=3000）for hexane were 0.36 L m^-2 h^-1 bar^-1and0.7 L m^-2 h^-1 bar^-1,respectively,and the rejection rates for paraffin were 78%and 56%under the condition of cross-flow.Because the commercial organic solvent nanofiltration membrane is homogeneous and non-porous membrane and the separation layer is thick,the permeance is low and the permeance performance is poor.Therefore,the graphene oxide-polyethylenimine（GO-PEI）lamellar composite organic solvent nanofiltration membrane developed by us can achieve a hexane permeance of9.26 L m^-2 h^-1 bar^-1 under cross-flow conditions,which is 25 times higher than that of commercial membranes,and the rejection rate of paraffin is improved to more than91%.The results show that the prepared lamellar composite membrane has good stability for long period of operation compared with the commercial membrane.